I downloaded a file from the bank with a csv extension. I was able to open it in Excel by double clicking and then save it with an xls extension. I was also able to import it as text. It does not appear to make a difference how the file was opened. The issue is the date format. The left column is the date expressed as an example 12/31/2012. Excel does not seem to recognize this as a date. It will not allow me to change to any other format such as 31-Dec-12.

Macbook Pro
Operating system OS X 10.6.8
Excel for Mac 2011